<?php
/**
 * Created by PhpStorm.
 * User: Guojunchen
 * Date: 2018/4/12
 * Time: 15:34
 */

namespace app\common\lib;

/**
 * Encryption 加密-解密类库
 * Class Encryption
 * @package app\common\lib
 */
class Encryption
{

    public static function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0)
    {
        $ckey_length = 4;

        $key  = md5($key ? $key : config('app.encryption_key'));
        $keya = md5(substr($key, 0, 16));
        $keyb = md5(substr($key, 16, 16));
        $keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length) : substr(md5(microtime()), -$ckey_length)) : '';

        $cryptkey   = $keya . md5($keya . $keyc);
        $key_length = strlen($cryptkey);

        $string        = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0) . substr(md5($string . $keyb), 0, 16) . $string;
        $string_length = strlen($string);

        $result = '';
        $box    = range(0, 255);

        $rndkey = array();
        for ($i = 0; $i <= 255; $i++) {
            $rndkey[$i] = ord($cryptkey[$i % $key_length]);
        }

        for ($j = $i = 0; $i < 256; $i++) {
            $j       = ($j + $box[$i] + $rndkey[$i]) % 256;
            $tmp     = $box[$i];
            $box[$i] = $box[$j];
            $box[$j] = $tmp;
        }

        for ($a = $j = $i = 0; $i < $string_length; $i++) {
            $a       = ($a + 1) % 256;
            $j       = ($j + $box[$a]) % 256;
            $tmp     = $box[$a];
            $box[$a] = $box[$j];
            $box[$j] = $tmp;
            $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
        }

        if ($operation == 'DECODE') {
            if ((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26) . $keyb), 0, 16)) {
                return substr($result, 26);
            } else {
                return '';
            }
        } else {
            return $keyc . str_replace('=', '', base64_encode($result));
        }
    }

    /**
     * 解密
     * @param $string
     * @param string $key
     * @return bool|string
     */
    public static function decode($string, $key = '')
    {
        return self::authcode($string, 'DECODE', $key);
    }

    /**
     * 加密
     * @param $string
     * @param int $expiry
     * @param string $key
     * @return bool|string
     */
    public static function encode($string, $expiry = 0, $key = '')
    {
        return self::authcode($string, 'ENCODE', $key, $expiry);
    }
}
